1.1 Field of the Invention
The present invention is directed toward novel clay-based pigments. More particularly, the invention relates to a modified kaolin pigment useful in the coating of paper for ink-jet printing applications.
1.2 Related Art
It is known that surface characteristics of paper (or any other printing surface) play a large role in how ink will be received and appear after application to the printing surface. Thus, varying print appearances can be expected depending on whether the surface ink is being applied to is uncoated or coated. Printing on uncoated paper results in low quality printing while printing on coated paper results in a higher quality print albeit of varying quality according to the nature of the paper coating composition.
Two of the more important characteristics to be controlled in color ink jet printing are depth of penetration and feathering or bleeding of the ink when applied to the paper. Too deep of a penetration results in poor color intensity. Bleeding results in poor printing definition. A further criteria, not known to have been identified in the prior art of multicolor ink jet printing and as hereinafter disclosed, is to control the contact angle of the various ink jet colors (i.e., cyan, magenta, yellow, and black) in a manner that the inks will substantially have the same contact angle when applied to the coated paper. When the contact angles of the various inks are substantially the same, the appearance of the ink colors are more uniform, i.e., one color does not appear more dull or more bright than another color.
A common component of paper coating compositions of the prior art is silica. While silica is an effective paper coating constituent as a hydrophilic pigment, it is somewhat more expensive than clay-based pigments and has severe rheological limitations such as in the amount of coating solids and Brookfield viscosity.
Thus, there is a need in the art for less expensive pigments which do not sacrifice printing qualities and desirably improve rheological properties.
U.S. Pat. No. 4,446,174 is directed to a method of ink jet recording and identifies desirable properties of substrates or coatings for satisfactory color ink jet printing. This patent purports that maintaining an R.sub.f value (ratio of traveling distance of dye to that of the solvent in the aqueous ink) of less than 0.59 produces images of high quality having high ink absorption and image density.
U.S. Pat. No. 4,792,487 describes ink jet recording medium coatings containing a high swelling montmorillonite clay and silica.
However, these references do not disclose or suggest the claimed combination of components of the applicants' invention.
We have now found a kaolin-based pigment which is less expensive than silica and provides outstanding color intensity and resolution in addition to several other advantages hereinafter described.